Bats under the radar

Gain a better understanding of the coronaviruses present in bats to better prevent, anticipate and cope with a possible new zoonosis. This is the aim of a project led by virologist Martine Peeters. Here's how it works.

Bats represent 20% of the world's mammals © Innocent Ndong (CREMER-IRD, Yaounde, Cameroon)

What do Covid-19, rabies and Ebola have in common ? For each of these diseases, the natural reservoir of the virus is the bat," explains Martine Peeters. When we follow the trail of an emerging infectious disease, we very often come across this little mammal", explains the virologist from the Translational Research in HIV and Infectious Diseases laboratory*. But why bats? " Bats account for 20% of the world's mammals, so when we're looking for the origin of a zoonosis, there's a one-in-five chance that it's the bat", explains the researcher.

Flying viral reservoirs

Present on every continent except Antarctica, these myriad chiropterans are veritable flying viral reservoirs. Thousands of viruses have been identified in bats, in 28 distinct viral families. One of these is the coronavirus family. " Most of the time, infection by these viruses is asymptomatic in bats, so the animal doesn't die from the disease, and can therefore disseminate the virus more effectively", explains Martine Peeters. And, as the only flying mammal, bats can move quickly and over long distances. "There is therefore a greater risk that they will transmit the viruses they carry to other species. Including humans.

"In the coronavirus family alone, 7 viruses have already been identified that have passed from bats to humans. While 4 cause common colds, the other 3 are responsible for Middle East Respiratory Syndrome (MERS-Cov) and severe acute respiratory syndromes due to SARS Cov-1 and SARS Cov-2, the famous coronavirus responsible for the Covid-19 pandemic. How did these viruses make the leap from bats to humans ? This inter-species passage can take place via an intermediate host or directly", answers Martine Peeters. Contacts between humans and chiropterans are in fact very frequent: "bats are hunted to be eaten or to make traditional remedies, children play with these animals, their guano is used for crops, fruit eaten by humans is sometimes contaminated by bat saliva, urine or feces...", explains the virologist. And the destruction of bats' natural habitat only increases the risk of inter-species transmission (see article "If we don't change, it will happen again").

10,000 bats

This list of 7 coronaviruses that have already been transmitted to humans is likely to grow in the near future. " To anticipate this eventuality, we need to know more about the diversity of coronaviruses circulating in bats", explains Martine Peeters. Accompanied by Guinean researcher Alpha Keita, the virologist aims to document the prevalence, genetic diversity and geographical distribution of coronaviruses in wild bats in Africa. The aim is to assess the risk of future zoonotic transmissions.

Researchers already have blood, saliva and faeces samples from over 10,000 bats in Guinea, Cameroon and the Democratic Republic of Congo. Thanks to this new project, they will be able to screen these samples for the presence of viral RNA or antibodies directed against coronaviruses, and thus estimate their prevalence. Another objective is to study the seasonality of these viruses. "If certain coronaviruses have a seasonal expression, we may not find them on spot samples. But we've been monitoring them monthly for a year, so we'll be able to look for the presence of viruses on each sample and determine any seasonality."

Reduce the risk of transmission

This is invaluable information for researchers: "in the event of seasonality, we'll be able to identify the times when viral excretion is highest, and thus determine the period at greatest risk of zoonotic transmission", explains the virologist. This more detailed knowledge of the coronaviruses present in bats would not only reduce the risk of transmission, but also enable us to identify the causative agent more rapidly in the event of a new zoonosis, "thanks in particular to targeted diagnostic tools". And if this epidemic scenario were to recur, the results of this ground-breaking project would offer the hope of developing a treatment or vaccine more rapidly. "We could, for example, work towards the development of a broad-spectrum vaccine. We will also have a better understanding of the targets of anti-viral drugs potentially effective against these coronaviruses, to identify or develop effective treatments".

Tools that everyone hopes they won't need. "The most important thing to limit the risk of new zoonoses is to limit contact between humans and the wild. Every man to his own home, and the coronaviruses will be well looked after.

* UMR TransVIHMI (UM, IRD, INSERM U1175, Université Check Anta Diop (Dakar, Senegal), Université Yaoundé 1 (Cameroon))